Speed limiting devices for motor vehicles are known. European Patent No. EP 260 372 describes a device for activating a speed limitation for motor vehicles in case of a failed or nonexistent vehicle speed signal using a signal corresponding to the engine speed as a basis for limiting the vehicle speed. In other words, by limiting the rotational speed (or r.p.m.) of the engine, typically by either cutting-off or reducing fuel supplied to the engine or by interrupting ignition, a speed limitation is achieved preventing the maximum allowable speed from being exceeded in the highest gear (high gearing ratio). This approach, however, does not rule out the problem of dangerous driving situations occurring when there is a failed speed signal, for example, when acceleration operations are completed in a low gear.
For instance, during a passing maneuver, where the goal is to complete the maneuver within a short driving distance, it is an expected reaction for the driver to shift to a low gear should oncoming traffic appear. In the lower gears, the driver can utilize the engine's full power to quickly complete the passing maneuver. However, even when the maximum r.p.m. is only briefly exceeded, a condition which can easily be withstood by present-day engines, an especially dangerous situation could arise if the fuel supply or ignition were to be cut off at that point.
Therefore, in cases where a signal indicative of the motor vehicle's speed is not available, it is desirable for engine cut-off not to be rigidly activated, as would occur when a constant rotational-speed threshold is exceeded. Rather, it would be beneficial for there to be a flexible speed limitation which would take into account the driving conditions that occur in each case so as to be better able to handle those driving situations where cutting-off the engine could create a safety hazard.